1. Field of the Invention
The invention relates generally to the field of communications, and particularly to methods and systems for implementing split numbering plan area codes in an IP Multimedia System (IMS) network.
2. Statement of the Problem
The growing number of subscribers and user equipment, such as land line telephones, fax machines and mobile phones has created phone number shortages in many area codes. An area code has a limited number of available phone numbers, and as the available number of phone numbers in an area code decreases, a new area code is needed to provide additional phone numbers for new subscribers.
When new area codes are created, it often becomes necessary to assign new phone numbers to existing subscribers when an existing area code is split into multiple area codes. Typically, the subscriber is assigned a new phone number corresponding to the subscriber's previous phone number with a new area code. For example, if the number of subscribers to be supported in area code “xxx” grows, the operator of the network can split the area into two area codes, such as “xxx” and “xx1”. The subset of existing subscribers for which the area code has changed will actually get a new phone number. For example, a subscriber with phone number xxx-ABC-DEFG will change to xx1-ABC-DEFG. Subscribers are given a grace period, which is mandated by the FCC, during which callers can either use the old or new phone number to access the subscriber. After the grace period ends, the subscriber can only be accessed using the new phone number.
In existing cellular networks, the home location register (HLR) maintains area code translation tables. The translation tables translate old phone numbers used by subscribers before the area code split into new phone numbers used by subscribers after the area code split. Thus, calls to the old phone numbers can be delivered to the new phone numbers. During the grace period, callers can dial the old phone number to access the subscriber. For example, in a wireless network, when the call arrives at the HLR, the HLR determines that the called phone number is not an active phone number. However, before declining the call delivery, the HLR looks up the called phone number in the numbering plan area code (NPA) translation table. If a matching phone number for the called phone number is found, the called number is translated to the corresponding new phone number, and the call delivery continues.
One problem with NPA translation tables is that they require additional software and set-up time for the HLR or switching center. Additionally, the NPA translation tables need to be removed from the HLR or switching center after the grace period is over. Unfortunately, current telephone network technology does not allow NPA splits without the use of translation tables.